Articles I like: Tracking Emerging Cryptomining Threats

The WordPress security plugin, Wordfence, published a blog entry describing how one of its techs working on cracking malware goes about doing the various steps in a recent day, analysing and developing responses to specific threats.

While the post seems at first to be highly technical, it’s quite readable by the informed layperson, and quite interesting to see. It also dispels the cryptocurrency baitclick headline to note it could have been running anything off the site, it just happened to be doing CCs.

Even the opening approach is quite illuminating, seeing the real work of defenders, not the Hollywood version.

One of our sources of threat data at Defiant is cleaning hacked websites. In this case, Ivan, a member of our SST team had cleaned a hacked site and handed me the forensic data for analysis. The site had been hacked for months before the owner discovered that it had been compromised.

My normal routine is to start by verifying the files we already detect to check if there is any new information inside any of them. Usually there is not, and this infection did not yield any surprises in the files that Wordfence already detected.

What did surprise me is that the server had a large number of malicious files we have not seen before. The server had been infected for a long time, which may have left the attacker feeling confident enough to upload more valuable code. For us, a server with code we have not seen before is a treasure trove, because it immediately allows us to add new detection capability to the Wordfence malware scanner. If an attacker is caught in this situation, they generally have a bad day, because many of their files that may have previously been undetected by malware scanners will now be detected by our scan.

The first thing that made this attacker different from others is that, instead of using a standard javascript code obfuscator that just scrambles the code, they were using a finite wordlist to replace variable and function names in the code. When you look at the code, the variable and function names just seem like gibberish.

I immediately searched for other similar files out of the remaining samples and found several, then proceeded to write new signatures to detect those files. That accomplished, I moved on to the next file in the list. That was a basic PHP file that selectively redirects regular users, not search engines, to a malicious website. This is a standard thing we see, so I wrote a signature to detect this updated malware variant and moved on.